Sylpheed runs on Unix-like systems such as Linux, BSD, and Mac OS X. It also supports Windows. Sylpheed uses GTK+ GUI toolkit. The newest version of Sylpheed works with GTK+ 2.4 or later (2.6 or later is recommended). Sylpheed is a free software distributed under the GNU GPL (the library part is GNU LGPL). You can freely use, modify and redistribute it under the license.

Features:

Simple, beautiful, and well-polished user interface

Comfortable operationality which is built in detail

Well-organized, easy-to-understand configuration

Lightweight operation

High reliability

Internationalization and Multilingualization support

High-level Japanese processing

Various protocols support

Security features (GnuPG, SSL/TLSv1)

Powerful filtering and search

Junk mail control

Flexible cooperation with external commands

What's new:

New features

New message notification window was added.

Icon theme feature was added.

SSL certificate hostname is validated now (#167).

PGP encrypt-to-self feature was added.

The feature to save message as plain text was added.

An option to the junk filter setting was added: 'Do not classify message as junk if sender is in the address book' (enabled by default) (#77)

Safe mode (which does not load plug-ins) was added (--safe-mode).

Improvements

The existence of destination folders are checked when creating a filter rule.

The recursion level is restricted up to 64 when scanning local mailbox (prevents infinite loop with symlink. Note: Linux automatically limits the symlink loop up to 40)